An operating procedure for the purposes of measuring unbalance to provide for unbalance compensation which is to be carried out on a rotary member to be balanced, in first and second compensating planes, provides that test runs are performed in which the effects of centrifugal forces which are generated by given test weights which rotate around the axis of the rotary member at given radii and in different planes perpendicular to the axis of the rotary member are measured in measuring planes, and are used for the purposes of calibrating the unbalance measuring system.
To carry out an unbalance measuring procedure on a rotary member which requires unbalancing, the rotary member can be mounted in a spring-mass system which is capable of vibration or oscillation in order to ascertain the compensating or balancing masses or weights required in first and second compensating planes, in a dynamic unbalance compensating operation. When carrying out the measurement operation, centrifugal forces which result from the unbalance of the rotary member produce movements which are perpendicular to the axis of the rotary member, or the mounting axis, in the oscillating system. The movements or centrifugal forces resulting from the rotary member unbalance are measured by measurement value sensors in measuring planes and corresponding electrical measurement signals are formed. When the measurement signals are evaluated, what is known as a plane separation apparatus is used to determine mass compensation in the compensating planes on the rotary member, in such a fashion that the oscillating movements at the mounting locations of the system are made zero.
It is known (German laid-open application (DE-OS) No 27 56 829 and the VDI publication 121 (1979) No 11, June, pages 585 through 589, G. Himmler, `Programmiertes Betriebsauswuchten anhand von Einflusskoeffizienten` [`Programmed operational balancing on the basis of correlation cofficients`]) to describe the transfer characteristics in respect of two unbalances U1 and U2 in two planes of the rotary member to two measurement value sensors in measuring planes which are different with respect to the two planes of the rotary member, and the signals X1 and X2 supplied by the measurement value sensors, by means of a linear equation system in accordance with the following matrix equation (1): ##EQU1##
The matrix elements a11, a12, a21 and a22 are correlation coefficients or influence coefficients which describe the characteristics of the unbalance measuring system. They form a correlation or influence coefficient matrix in respect of the linear equation system.
To provide for plane separation, the equation system (1), in respect of the unknown unbalances U1 and U2, is solved in accordance with the following equation system (2): ##EQU2##
The measuring signals X1 and X2 are ascertained as measuring parameters, in the unbalance measuring operation. The correlation coefficients have to be determined by system identification. As is known from the VDI publication 121 (1979), No 11, June, pages 585 through 589, or the publication Hofmann Info 9 (impressum 9632 098 08-77), that is effected by first inserting a test weight into the one compensating plane of the rotary member and measuring the resulting effects (forces or movements) in two measuring planes. Then, a second test weight is inserted into the other compensating plane of the rotary member and the resulting effect (forces or movements ) are ascertained in the two measuring planes. Those measurement values and the test unbalances are then used to calculate the correlation or influence coefficients which form the matrix elements of the above-indicated linear equations (1) and (2), the latter then being evaluated for the purposes of plane separation.
So that the solutions of equation system (2) are clear, linear independency of equation system (1) is required, in other words, the determinant of the correlation coefficient matrix is not equal to zero. As different types of rotary members are measured in unbalance measuring assemblies, it is inevitable that a measuring plane comes to lie at the center of vibration or vibration node of the measuring system or that one of the two measuring planes is at an only small distance relative to the node of the measuring system. If the measuring plane is at the vibration node, that situation involves a singular state and the determinant of the coefficient matrix becomes zero. No plane separation is then possible. In situations in which one of the two measuring planes is at a small distance relative to the node of the system, the determinant of the coefficient matrix becomes of low value so that in terms of determining unbalance phenomena numeric difficulties occur and the measuring system has only poor plane separation characteristics.
As is known from EP 0 133 229 B1, it is possible for test weights to be arranged in a plurality of successive, axially spaced-apart calibration planes and to carry out a plurality of test runs. Calibration data are derived from the plurality of test runs, and such data can be used to reduce the error component of the detected unbalance in predetermined unbalance correction planes. It will be appreciated however that the plurality of test runs or calibration runs required with that operating procedure involves a high level of expenditure in terms of time and trouble in carrying the process into effect.